Androgen-binding (ABP) is produced by the Sertoli cells of the testis. Although the function(s) of ABP is unknown, the possibility that it may be involved in spermatogenesis, in sperm maturation, or in the regulation of epididymal function has prompted extensive research on the molecule. ABP may also serve as a marker for Sertoli cell function. Since these cells are intimately associated with the developing germ cells, information regarding their function could be of value in diagnosing cases of infertility and for developing agents that interfere with Sertoli cell or ABP function thus leading to methods of male contraception. We propose to perform the following studies in immature (25 day-old) and adult male rats: 1) To use photoaffinity labeled ABP and immunochemical methods to study the distribution, fate, and metabolism of ABP. 2) To determine whether membrane receptors for ABP can be detected in potential target tissues under in vitro conditions. 3) To examine the physicochemical nature of ABP in plasma and compare it with ABP in the testis-epididymis compartment. and 4) To develop polyclonal antibodies against ABP to identify and quantitate it in tissues and fluids, and to obtain information on its possible function. A comparison of the distribution of bioreactive (measured using photolabeled ABP) and immunoreactive ABP will provide information on its sites of utilization or degradation. Autoradiography at the EM level could elucidate the cell biology of ABP uptake. We will study the specificity and kinetics of the interaction of [125I] ABP with homogenates and/or membrane fractions from potential target tissues to determine if classical receptors exist for ABP. The comparison of ABP from plasma and the testis-epididymis will be done using denaturing and non-denaturing PAGE, isoelectricfocusing, ion exchange chromotography, and immunological techniques. These studies will reveal the physicochemical nature and microheterogeneity of bioreactive ABP's. If neutralization of endogenous ABP leads to discrete alterations in reproductive function (e.g., changes in spermatogenesis, in epididymal morphology, or in sperm maturation), information on the function of ABP will be obtained. The proposed studies will provide unique information concerning similarities and differences that might exist between bioreactive and immunoreactive forms of the molecule and on the role of ABP in male reproductive function.